After the pre-treatment of desulfurization, desiliconization and dephosphorization, the liquid iron will produce a great amount of solid slag which float on its surface. The solid slag must be removed away promptly. Otherwise it may impair the pre-treatment effect for the liquid iron, leading to the rise in production cost of the next processes.
The existing slagging-off device in the process of pre-treatment of liquid iron has been used since the 1950s or 1960s. This kind of slagging-off machine for liquid iron is of linear reciprocating type, driven mechanically or hydraulically. A slag rake, which is made of refractory material, is mounted on a cantilever of the machine. By immersing the rake into the liquid iron to a certain depth and making it moving along the surface of liquid iron in linear or curved reciprocating manner, it can rake out the solid slag floating on the surface of liquid iron in the ladle gradually.
However, the conventional slagging-off technique and the equipment have disadvantages as follows: (1) Long time taking for the work of slagging-off and low working efficiency. Normally, it would need to reciprocate for over ten or even tens of times, which takes 5 to 10 minutes; (2) Incomplete deslagging and low deslagging rate. By adding slag adhesive agent or slagging-off agent so as to conglomerate the slag, the deslagging rate can just reach 80% to its maximum. The incomplete deslagging would directly bring about much more resulfurization in converter or electric furnace; (3) Liable to carry away liquid iron while raking out slag, generally with an iron loss between 0.5% and 1.0%. These problems have already become the worldwide problems that trouble the international iron and steel industry and constrain the development in this field. The direct economic loss incurred thereof is over 0.5 billion US dollars each year.
Over the recent years, rapid development has seen in China's iron and steel industry, with an overall yield reaching the first place in the world. It was estimated that pretreatment amount of liquid iron could reach 50 million tons in 2003. But, as the technology and equipment are relatively backward, the actual iron loss rate is mostly around 1.0%. Together with the economic loss caused by resulfurization in converter and electric furnace, the direct economic loss a year would be over 0.5 billion RMB.